As is well known in the capacitor art, an electrolytic capacitor structure commonly employed comprises a cylindrical metal can or container closed at one end and open at the other, various internal capacitor elements contained within the can including an electrolyte, and a header for closing the open end of the can. The header, also referred to as an end cap, may be provided with one or more terminals.
In assembly, the closure is normally obtained by inserting a disc-shape header into the open end of the can until it engages a radially inwardly projecting bead or shoulder on the inner cylindrical wall of the can adjacent its open end. This shoulder acts as a stop to prevent further axial insertion of the header. To lock the header in place in the can, the extreme or marginal end of the can is spun over or crimped about the peripheral edge of the header. Commonly, the axially outer end of the header at its peripheral edge is recessed to accommodate a separate-piece rubber gasket which is placed under compression by the spun-over or crimped marginal end of the can to seal the can against loss of electrolyte as well as entrance of moisture, air and other contaminants.
The header often is made of an insulative material which ordinarily is a molded synthetic resin of the phenolic class. The phenolic header when assembled in the capacitor heretofore has been in contact at its axially inner end with the electrolyte contained within the can. This direct contact may cause loss of electrolyte by diffusion through the end cap and/or contamination of the electrolyte by absorption of impurities from the phenolic header. This loss and contamination will usually lead to variation and degradation of electrical properties of the capacitor, as well as premature break-down. The loss of electrolyte further may be aggravated by one or more electrical terminals inserted or embedded in the cap which provide for an electrical connection through the cap. The inner and outer ends of the terminals are exposed respectively to the interior and exterior of the can and hence any continuous gaps between the phenolic body and terminals inserted or embedded therein provide a path for leakage of electrolyte from the interior of the can. This leakage may be even more pronounced in a capacitor subjected to widely fluctuating temperatures since the metal terminals and phenolic body have different thermal expansion characteristics potentially resulting in wider gaps therebetween.
The elimination of the above noted drawbacks in such electrolytic capacitor construction is a principal object of the present invention as is the provision of a more effective seal between the header and terminal therein.
It is another object of the invention to provide a capacitor end cap or header capable of achieving the aforenoted objects which may be easily and inexpensively fabricated, and then assembled in the capacitor can in conventional manner.